Analysis of hybrid wavelength hopping/time spreading systems and their classification into symmetric and asymmetric systems (undercolored and overcolored asymmetric systems) is given. The characteristics of a hybrid system using extended quadratic congruence sequences for spreading and prime sequences and their cyclic shifts for hopping are examined. It is shown that the sequences exhibit excellent cross-correlation properties even in the case of a general asymmetric overcolored system. Analysis of the security properties of hybrid systems is presented both from the viewpoint of exhaustive search and from the viewpoint of chosen attack. Initial investigations indicate that the system can be so configured to allow high level of protection against determined attack, with this being especially true for an asymmetric system. Because of the massive number of users the system can support, the proposed scheme is suitable for large optical LAN's with increased security demands.

Hybrid wavelength hopping/time spreading schemes for use in massive optical networks with increased security

An optical orthogonal signature pattern code (OOSPC) is a collection of (0,1) two-dimensional (2-D) patterns with good correlation properties (i.e., high autocorrelation peaks with low sidelobes, and low cross-correlation functions). Such codes find applications, for example, to parallelly transmit and access images in "multicore-fiber" code-division multiple-access (CDMA) networks. Up to now all work on OOSPCs has been based on an assumption that at most one pulse per column or one pulse per row and column is allowed in each two-dimensional pattern. However, this restriction may not be required in such multiple-access networks if timing information can be extracted from other means, rather than from the autocorrelation function. A new class of OOSPCs is constructed without the restriction. The relationships between two-dimensional binary discrete auto- and cross-correlation arrays and their corresponding "sets" for OOSPCs are first developed. In addition, new bounds on the size of this special class of OOSPCs are derived. Afterwards, four algebraic techniques for constructing these new codes are investigated. Among these constructions, some of them achieve the upper bounds with equality and are thus optimal. Finally, the codes generated from some constructions satisfy the restriction of at most one pulse per row or column and hence can be used in applications requiring, for example, frequency-hopping patterns.

Two-dimensional spatial signature patterns

In this paper, an architecture for code-empowered optical CDMA (OCDMA) lightwave networks is presented. The architecture is based on reconfigurable optically transparent paths among users of the network to provide high-bandwidth optical connections on demand over small areas such as local area networks or access networks. The network operates on the transmission of incoherent OCDMA codes, each network station being equipped with an OCDMA encoder and decoder. The routing at a network node is based on the OCDMA code itself. The destination address, as well as the next node on the path, is given by the code as in a code-empowered network. A node consists of an OCDMA router built from parallel code converter routers that perform switching, routing, and code conversion. The latter enables a virtual code path for increased scalability. Commonly available delay lines enable the tunability of the encoder, decoder, and router for a reconfigurable and flexible network. Flexibility and granularity are also accentuated by OCDMA encoding. An OCDMA lightwave network can therefore respond to changes in traffic load, traffic conditions, failure, and other network impairments. We describe the possible architectures and the routing constraints of such OCDMA lightwave networks. We present a power analysis and focus on the performance issues of dynamic routing. The effect of coding, topology, load condition, and traffic demand is analyzed using simulations. The obtained results show that the flexibility of OCDMA and the large offered cardinality can be a solution to the needs of local area and access networks.

Code-Empowered Lightwave Networks

To transmit digitized image pixels in optical code-division multiple-access (CDMA) networks with multicore fiber, classes of two-dimensional (2-D) patterns, so-called optical orthogonal signature pattern codes (OOSPCs), have previously been proposed. The new technology enables parallel transmission and simultaneous access of multiple 2-D images in multiple-access environments. In this letter, we construct two new families of "double-weight" OOSPCs without the assumption of identical weight for all signature patterns in a code set. Since the performance of a signature pattern varies with its weight, these new double-weight OOSPCs are especially useful for optical CDMA networks with multiple performance requirements.

Double-weight signature pattern codes for multicore-fiber code-division multiple-access networks

Methods and apparati for spatially encoding and decoding spread spectrum communication signals using broad band light sources are disclosed. The encoding algorithms involve the use of orthogonal spatial wavelets, which are preferably discrete attenuation functions of light from different sources so that the discrete attenuation function is imposed upon the spectrum of the light source. The function may be used either merely for providing an encoded channel or by providing a second mask that may be, for example, the complement of the discrete attenuation function so that the light beam is discrete with the first attenuation function.

High capacity spread spectrum optical communications system

A method for optical signaling is investigated that allows multiple transmitters to simultaneously use the same noncoherent receiving aperture. The signaling is based on the properties of laser speckle interference patterns. Capacity for an interference limited system is explored for a correlation receiver based on random coding. A synchronization scheme is presented that allows a practical implementation of the proposed optical multiple access system. >

A.A. Hassan

Papers

Spatial optical CDMA